fix(deps): update rust crate base64 to 0.21.3

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
base64	dependencies	patch	0.21.0 -> 0.21.3

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Release Notes

marshallpierce/rust-base64 (base64)

v0.21.3

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• Implement source instead of cause on Error types
• Roll back MSRV to 1.48.0 so Debian can continue to live in a time warp
• Slightly faster chunked encoding for short inputs
• Decrease binary size

v0.21.2

Compare Source

• Rollback MSRV to 1.57.0 -- only dev dependencies need 1.60, not the main code

v0.21.1

Compare Source

• Remove the possibility of panicking during decoded length calculations
• DecoderReader no longer sometimes erroneously ignores padding #​226

Breaking changes

• Engine.internal_decode return type changed
• Update MSRV to 1.60.0

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